The present invention relates to a method for retrieving metallic vapor from a mixture gas which contains said metallic vapor, and to a device for practicing said method; and more particularly relates to a method for retrieving, from a mixture gas which has been produced by a reduction reaction of an oxide of a metal and which contains vapor of said metal and oxidizing gas also produced as a result of said reduction reaction, said metallic vapor in a liquid state, and to a device for practicing said method.
A known method of preparing a metal in the pure state is to reduce an oxide of the metal by heating this oxide to a high temperature along with a reducing material which then preferentially combines with the oxygen in said oxide, thus abstracting said oxygen from the oxide and leaving the metal in pure form. At such a high temperature the metal is left in the form of metallic gas or vapor, and this vapor is mixed with the other products of the reduction reaction, i.e. with a compound or compounds of the oxygen and the reducing material. Thus, the question arises as to how the metallic vapor can be cooled down and separated from the product of the reduction reaction, without the reverse or oxidizing reaction occurring, i.e., without the metallic vapor recombining with the reduction reaction product. This reverse reaction can easily occur, especially in the case of certain metals such as for example magnesium.
In the case of metals which have a relatively low tendency to undergo the reverse or oxidizing reaction, and which have a low melting point, such as for example zinc, there has been practiced a prior art retrieval method in which the high temperature mixture gas consisting of the gaseous products of the reduction reaction including zinc vapor has been introduced into a condenser containing a mass of molten metal having a fairly low temperature which is lower than that of the mixture gas, and in which the metallic vapor in the mixture gas has been condensed into liquid by the molten metal being contacted intimately with the mixture gas by being splashed with a stirrer or paddle or impeller or the like. Thereby, the metallic vapor is rapidly cooled and is picked up by the molten metal. As a variation of this prior art method, it has been known for the condenser to be shaped as a U-shaped tube, with the molten metal for retrieval contained in the bend of the tube, and for the mixture gas consisting of the gaseous products of the reduction reaction including the metallic vapor to be blown around this U-shaped tube, being bubbled through the molten metal for retrieval.
This prior art method is effective for retrieving the vapor of a metal such as zinc which has a relatively low tendency to undergo the reverse or oxidizing reaction and which has a low melting point, but it does not work well in the case of retrieving the vapor of a metal such as magnesium or calcium which has a relatively high tendency to undergo the reverse or oxidizing reaction and which has a high melting point. In such a case, when this method is applied to retrieving the vapor of (for example) magnesium or calcium, the reverse or oxidizing reaction occurs to such an extent that both the purity of the retrieved metal and also the efficiency of retrieval are unacceptably low. Therefore, as far as these metals are concerned, this method is not of practical use for retrieving their vapors.
Another prior art method for retrieving metallic vapor from the gaseous products of a reduction reaction including said metal vapor has been the so called gas cooling method, in which a large volume of natural gas or hydrogen gas has been blown into and mixed with said gaseous products of the reduction reaction which are at a high temprature, so as rapidly to cool them. However, with such a retrieval method, it is very difficult completely to prevent the reverse reaction occurring, and according to this the purity of the retrieved metal is low, about 50% or so in the case of a continuous process. Further, this method has the additional disadvantage of having a high cost, since a large volume of gas for cooling is required.